This invention relates to systems for determining performance characteristics of extrudable solid materials subjected to compressive forces. More particularly, the invention relates to devices designed to measure lateral expansions of vehicular gaskets for purposes of determining performance or functional limits of such materials.
In continued efforts to find improved materials for use in gaskets, it is necessary to test various proposed materials. One such test involves compression of a material specimen until it begins to extrude laterally. The point at which lateral extrusion becomes significant defines the point at which the material has reached its functional limit for gasketing purposes.
In order to perform lateral extrusion tests, compression platens are typically used in conjunction with mechanical fixtures to provide high compressive forces on test specimens. Such tests are generally performed on circular discs of materials having various specified areas and thicknesses. Generally a specimen is squeezed between two opposed platens, under an increasing compressive force applied by means of a hydraulic ram. As a result, the specimen decreases in thickness over the force cycle. Generally, at some point, the circumference, hence diameter, of the specimen (even of a fibrous material) will begin to increase.
In the past, it has been necessary to monitor the diameter of a test specimen at intervals during the test cycle with either a ruler or calipers. If a specimen had not reached a pre-determined diameter change at a given load, the test was repeated at higher loads until the onset of significant extrusion was realized. This reiterative process continued until the functional limit of the material was ultimately reached. Such trial and error method was not only time consuming, but did not lend itself to modern statistical analyses.